I'm stuck with a problem regarding hybrid stepping motors and I'm not sure where I'm wrong.
I can't reconcile the torque constant with the maximum speed of a hybrid stepping motor with the following nameplate:
Holding torque = 9 Nm
Rated current = 10 A
Steps/rev = 200
Rated power = 40 W
The problem, in short, is this. The torque constant of this motor is 0.9 Nm/A, which (give or take some possible coefficients due to the multiphase nature of the machine or to the sinusoidal nature of the back-emf) is also the voltage constant in V/(rad/s) that yields the back-emf given the speed. The data sheet also gives the torque/speed characteristic: with a 24 V supply, the maximum speed is 6000 pps. With 200 steps/rev, 6000 pps is 30 rev/s, or 188 rad/s (mechanical). Now, if we multiply 188 rad/s times the voltage constant of 0.9, we get 169 V! How on Earth can a motor run on 24 V when its back-emf is 169 V? It should never be able to reach such speed.
I tried to write this off as a mistake in the data sheet, but then all the data sheets from this manufacturer must be wrong. Moreover, I found another data sheet from another manufacturer with the same problem (too high maximum speed given the supply voltage and machine constant).
What am I doing wrong? Thanks in advance to anyone who can shed some light.